Now cite a case in which a court found that a State's exercise of its police powers to regulate possession of something within its borders constituted a regulation of commerce.

That would be Brown v. Maryland - 25 U.S. 419 (1827) where the State of Maryland used it's police power to require a license for the importation and wholesale of " foreign goods by the bale or package, &c."....

Nope. That is a clear and direct attempt to regulate commerce (i. e., commercial activity). It has nothing to do with the possession by an individual of personal property for his own use.

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"It is long been a principle of ours that one is no more armed because he has possession of a firearm than he is a musician because he owns a piano. There is no point in having a gun if you are not capable of using it skillfully." -- Jeff Cooper